Parents’ verbal interactions with babies have long been linked to infant language development. Previous studies show that children speak and understand more words and sentences when they have verbal interactions with parents and caregivers. But less is known about how the tone and tempo of parents’ speech might impact early language development for kids.

The current study focused on what researchers dub “parentese,” a speaking pattern common in many languages that is characterized by higher pitch, slower tempo and exaggerated intonation. Researchers randomly assigned 71 families with normally-developing babies to either receive coaching in how to speak to infants, with a focus on “parentese,” or to go without coaching.

“Providing parents with knowledge and feedback on their own language practices, and with concrete tips on when and how to talk to their infants, changed how they talked to their infants, and this was associated with immediate as well as longer-term positive impacts on the babies’ language skills,” said lead study author Naja Ferjan Ramirez of the University of Washington in Seattle.

At the start of the study, when babies were 6 months old, researchers recorded families over a 12-hour day to assess how many words parents spoke to infants, how many back-and-forth exchanges occurred between parents and kids, and how parents sounded. They did additional recordings when babies were 10, 14 and 18 months old, also assessing what babbling and pre-language sounds kids made and how many words kids understood and used.

Families assigned to coaching had sessions when babies were 6, 10 and 14 months old. These were designed to encourage use of “parentese” and back-and-forth exchanges with their babies. Coaches also discussed language development milestones and how to help babies reach these targets.

Coaching had the intended effect: families spoke more “parentese” when they received coaching. Coaching was also associated with more back-and-forth exchanges between parents and babies, and more advanced language development by 18 months. Toddlers in families that received coaching spoke more words, and had more complex language interactions.

While some previous research suggests that babies might develop language more slowly in families with less income or education, the current study found gains associated with coaching were similar across socioeconomic groups.

One limitation of the study is the potential for family members who know they’re being recorded to pay closer attention to their speech and interactions with babies than they might outside of a trial setting, the study team notes in the Proceedings of the National Academy of Sciences.

Still, the results highlight the critical role that parent-child engagement plays in child speech development and demonstrate that changes in adult speech patterns can improve child outcomes, said Dr. Caroline Kistin, a researcher at Boston Medical Center and Boston University School of Medicine who wasn’t involved in the study.

Parentese, which is common in many languages and cultures, may help capture infants’ attention and make it easier for them to differentiate between sounds, Kistin said by email.

“Parentese also appears to engage infants differently than other types of speech, and the slow speed may afford more opportunities for back and forth conversational turns between parents and young children,” Kistin said. “These interactive back-and-forth patterns have been shown to be particularly important for early language development, and some studies suggest the pattern of parent-child interaction is likely much more important than total number of words heard.”